Today in chemistry history graphic on Robert Bunsen and the Bunsen burner. The graphic shows an annotated diagram of the Bunsen burner that highlights its key features.
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The Bunsen burner is one of the ubiquitous symbols of chemistry. Though it might be a rarer sight in university laboratories these days, due to some of the highly flammable substances used, they’re still very commonly found in school science classrooms, and for most of us probably bring back memories of school science lessons. As today is Bunsen Burner Day, this graphic takes a quick look at the burner’s anatomy, and we’ll discuss its history in a little more detail below.

Note: this is an updated version of a post previously published in 2016.

Firstly, a word on the choice of date for Bunsen Burner Day. This coincides with the anniversary of the birth of its creator, Robert Bunsen – or, at least, it’s intended to. There’s actually some confusion over Bunsen’s birth date, with some documents stating it’s in fact on the 30th of March, whereas others state the 31st. Even more confusingly, though his own hand-written CV is one of the documents that gives his birth date as the 30th, it was claimed by his biographer that Bunsen commonly celebrated his birthday on the 31st.

Though his birthdate may remain unclear, Bunsen’s contribution to science in the shape of his development of the Bunsen burner is well documented. His design actually drew on and developed an earlier one created by Michael Faraday, which he and his laboratory assistant Peter Desaga subsequently refined. Bunsen wanted to create a device that would produce a flame with very little soot, a criterion that the burner he and Desaga designed was able to meet.

A sooty flame burns yellow or orange; this is due to the presence of carbon atoms in the soot, which glow yellow when heated to a high temperature. This was problematic for Bunsen, as he wanted to study the colours of light emitted when different elements were heated – but this was impossible with the colour from the incandescent carbon atoms masking any other colours. His new burner could have the flow of air into it adjusted. When its air hole was closed, a low-temperature sooty flame was produced due to the incomplete burning of the gas fuel. However, when the air hole was open, more air could flow into the burner, and hence more oxygen was available, allowing the gas to burn completely and preventing the generation of soot particles.

When an element sample is heated, it can absorb energy from the flame, and the electrons in the atoms in the sample can gain this energy – they become what chemists refer to as ‘excited’, jumping up to higher electron energy levels within the atom. However, this is a fleeting state. The electrons soon fall back down to their original positions from these higher energy levels. When they do so, they release their excess energy in the form of light, creating a characteristic emission. The exact pattern of light produced in the emission spectrum is unique for different elements – essentially an element’s ‘fingerprint’ – and so it can be used to determine an element’s identity.

This is exactly what Bunsen did. Using his burner along with a spectroscope to allow him to see the different wavelengths of light given off by heated samples, he was able to identify the emission spectra of different elements. Using this process, he discovered two previously unknown elements: caesium in 1860, and rubidium in 1861. Students commonly repeat a similar process using his eponymous burner in schools today. Solid compounds can be held in a Bunsen flame, or solutions can be sprayed into the flame, to produce coloured flames that are characteristic of particular elements, allowing them to be identified.

The emission spectra of elements don’t just have applications in the science laboratory, either. They’re also used by astronomers to identify the elemental constituents of distant stars. Without being able to interpret these spectra, it’d be next to impossible to determine the constituents of stars – but with them, we can confidently determine the composition of stars hundreds of light years away.

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References & Further Reading

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